There exist cabinets with an external fire resistant housing comprising one or more layers of fire resistant material such as gypsum, concrete and the like. These layers form a heat barrier. The degree of protection depends on the thickness, the kind and amount of the materials used. In addition to these physical facts concerning the walls of the cabinet often other factors are also of importance. If for example magnetic tapes, floppy discs or microfilms must be stored, their sensitivity to moisture or their inflammability must be taken into consideration.
In the U.S. Pat. No. 3,559,594 a cabinet with heat insulated walls is described in which a further cabinet is provided which has walls with a filling of a heat absorbing material, e.g. sodium acetate trihydrate which melts at approximately 58.degree. C. and absorbs large amounts of heat. Sodium metasilicate is also of advantage (German published application No. 24 13 644). To keep as much as possible heat from entering the interior of the cabinet, it is necessary to avoid empty spaces in the filling. In the cited U.S. Pat. No. 3,559,594 it is taught to fill the spaces completely by casting liquid sodium acetate trihydrate. The casting has the disadvantages that it does not avoid hollow spaces in the form of enclosed air bubbles. Further, the casting is a manufacturing method requiring much skill and relatively long cooling times. There is also always the danger of spilling of hot filling material. In cooling there is shrinkage of the material which may also lead to undesirable hollow spaces.
The German Pat. No. 22 45 453 teaches to provide in the interior of a cabinet with heat resistant walls a container having walls formed by cells filled with sodium acetate trihydrate in particulate form. The manufacturing of this cell must not take place by casting hot material, but can take place by filling-in a certain amount of particulate material at room temperature Because, when the cabinet is transported, the particulate material can settle somewhat, a relatively large hollow space is obtained at the top. In the case of a fire, melting of the particulate material may increase this hollow space. In order to avoid that heat may enter into the container, heat conducting elements are provided in the hollow space. These heat conducting elements extend into the heat absorbing material to transfer the heat into this material. This prior art heat resistant cabinet has not only the disadvantage that it is relatively complicated and expensive, but in the case of a fire there exists also the danger of leaking of liquid sodium acetate trihydrate. The leaking liquid may eventually damage the stored articles. If it is desired to prevent leakage of liquid material, the cell must be manufactured watertight. However, this is an additional expense.
German Pat. No. 22 45 453 further reports on tests with different mixtures comprising different amounts of further materials, for example particulate vermiculite, particulate perliteor or fine saw-dust. These further materials have the purpose to alter the heat regulating effects of the sodium acetate trihydrate. U.S. Pat. No. 3,762,787 discloses the use of sodium acetate trihydrate as a heat absorbing substance and further discloses the addition thereto of varying amounts of heat resistant materials, such as particulate vermiculte, particulate perlite or fine saw-dust for variation of the heat regulation characteristics, and in the case of the addition of insulative materials such as vermiculate, to provide a heat barrier in the same physical location as the heat sink.